Lens barrel and imaging device

ABSTRACT

The lens barrel is a lens barrel for forming an optical image of a subject on an imaging element, comprising a first lens unit, a second lens unit, a focus lens unit, a zoom mechanism, and a focus actuator. The focus lens unit is movably supported by the second lens unit in the optical axis direction. The operating force inputted to the zoom control is mechanically transmitted to at least one of the first lens unit and the second lens unit. The focus actuator is fixed to the second lens unit and electrically drives the focus lens unit relative to the second lens unit in the optical axis direction. The second lens unit or the focus lens unit is disposed nearest to the image plane in the optical system including the first lens element, the second lens element, and the focus lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2008-232040 filed on Sep. 10, 2008. The entire disclosure of JapanesePatent Application No. 2008-232040 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The technical field relates to a lens barrel with which a focal lengthcan be changed.

2. Description of the Related Art

Digital single lens cameras with which an optical image of a subject canbe converted into an electrical image signal and outputted have rapidlygrown in popularity in recent years. This type of digital single lenscamera generally has an interchangeable lens configuration, with whichlenses can be attached and removed.

A high-magnification zoom lens system is sometimes employed in aninterchangeable lens unit. With a telephoto zoom lens system, becausethe focal length of the telephoto end is long, the overall opticallength (the distance from the image plane to the apex of the lenssurface nearest to the object) also tends to be longer. Accordingly, thefocusing of a telephoto zoom lens system is generally done by moving afirst lens group nearest to the object.

However, since the lens group nearest to the object is larger than theother lens groups, it is difficult to raise the drive speed of the lensgroup, which means it is harder to increase the autofocus speed.

In view of this, as disclosed in Japanese Laid-Open Patent Application2006-10991, for example, an interchangeable lens unit has been proposedin which a linear actuator is used to drive the focus lens groupdisposed nearest to the image plane.

With the digital camera discussed in Patent Document 1, however, it isnecessary to provide a focal plane shutter between the imaging elementof the camera body and the lens group nearest to the image plane in theinterchangeable lens unit, so the back focus of the optical system (thedistance between the imaging sensor and the lens nearest to the imageplane) has to be made longer. In this case, to accommodate a telephotozoom lens system, the distance that the focus lens group moves in theoptical axis direction must also be increased corresponding to the zoomratio.

With a conventional method, however, since the focus lens group ismovably supported by a fixed frame, to ensure enough movement of thefocus lens in the optical axis direction, space for this movement has tobe provided ahead of and behind the focus lens group, and this tends tomake the optical system larger.

In other words, with a conventional lens barrel, it was difficult toincrease the speed of autofocusing and to reduce the size at the sametime.

SUMMARY

The lens barrel according to an aspect is a lens barrel for forming anoptical image of a subject on an imaging element, comprising a firstlens unit, a second lens unit, a focus lens unit, a zoom mechanism, anda focus actuator. The first lens unit includes a first lens element anda first lens support frame supporting the first lens element. The secondlens unit includes a second lens element arranged to vary the focallength by moving relative to the first lens element in the optical axisdirection, and a second lens support frame supporting the second lenselement. The focus lens unit includes a focus lens arranged to vary thefocal state of the optical image by moving relative to the first lenselement or the second lens element in the optical axis direction, and afocus lens support frame supporting the focus lens, the focus lenssupport frame being movably supported by the second lens unit in theoptical axis direction. The zoom mechanism is a mechanism arranged torelatively move the first lens unit and the second lens unit in theoptical axis direction, including a zoom control arranged to be operatedby the user, with which the operating force inputted to the zoom controlis mechanically transmitted to the first lens unit and/or the secondlens unit. The focus actuator is fixed to the second lens unit and isconfigured to electrically drive the focus lens unit relative to thesecond lens unit in the optical axis direction. The second lens unit orthe focus lens unit is disposed nearest to the image plane in theoptical system including the first lens element, the second lenselement, and the focus lens.

With this lens barrel, when the zoom control is operated, the secondlens unit is moved in the optical axis direction by the zoom mechanism,for example. Since the focus lens unit is supported by the second lensunit, the focus lens unit moves along with the second lens unit in theoptical axis direction. Accordingly, the amount of movement of thesecond lens unit with respect to the imaging element can be utilized asthe amount of movement of the focus lens unit with respect to theimaging element. Consequently, even though a large space is not providedahead of and behind the focus lens unit, there will still be enoughmovement of the focus lens unit.

Furthermore, the second lens unit or the focus lens unit is disposednearest to the image plane in the optical system including the firstlens element, the second lens element, and the focus lens. Accordingly,the second lens unit and the focus lens unit are disposed near the imageplane in the optical system, which allows the focus lens to be smaller.Using a smaller focus lens allows the drive speed of the focus lens unitto be raised.

Thus, with this lens barrel, faster auto-focusing and a smaller size canboth be achieved.

The lens barrel here encompasses not only a type that is integrated witha camera body, but also an interchangeable lens unit used in aninterchangeable lens type of imaging device. Imaging devices includethose in which a camera body and a lens barrel are integrated, as wellas interchangeable lens imaging devices. Examples of imaging devicesinclude digital still cameras, interchangeable lens digital cameras,digital video cameras, portable telephones with a camera function, andPDAs (Personal Digital Assistants) with a camera function. The imagingdevice encompasses devices capable of capturing only still pictures,devices capable of capturing only moving pictures, and devices capableof capturing still pictures and moving pictures.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a simplified diagram of a digital camera;

FIG. 2 is a block diagram of the configuration of a camera body;

FIG. 3 is a simplified oblique view of a digital camera;

FIG. 4A is a top view of a camera body, and FIG. 4B is a rear view of acamera body;

FIG. 5 is a cross section of an interchangeable lens unit (wide angleend);

FIG. 6 is a cross section of an interchangeable lens unit (wide angleend);

FIG. 7 is a cross section of an interchangeable lens unit (telephotoend);

FIG. 8 is a cross section of an interchangeable lens unit (telephotoend);

FIG. 9 is an exploded oblique view of a second lens group unit and afocus lens unit;

FIG. 10 is an exploded oblique view of a second lens group unit and afocus lens unit;

FIG. 11 is a simplified cross section of a focus motor;

FIG. 12 is a tracking table for realizing a zoom lens system;

FIG. 13 is an oblique view of the area around an electrical substrateand a lens mount contact; and

FIG. 14 is a plan view of the area around an electrical substrate and alens mount contact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

First Embodiment Summary of Digital Camera

A digital camera 1 will be described through reference to FIGS. 1 to 12.FIG. 1 is a simplified diagram of the digital camera 1. As shown in FIG.1, the digital camera 1 (an example of the imaging device) is a digitalcamera with an interchangeable lens, and mainly comprises a camera body3 and an interchangeable lens unit 2 (an example of the lens barrel)that is removably mounted to the camera body 3. The interchangeable lensunit 2 is mounted via a lens mount 95 to a body mount 4 provided to thefront face of the camera body 3.

FIG. 2 is a block diagram of the configuration of the camera body 3.FIG. 3 is a simplified oblique view of the digital camera 1. FIG. 4A isa top view of the camera body 3, and FIG. 4B is a rear view of thecamera body 3. FIGS. 5 to 8 are simplified cross sections of theinterchangeable lens unit 2. FIGS. 5 and 6 show the state at the wideangle end, while FIGS. 7 and 8 show the state at the telephoto end. FIG.6 is a cross section in a different plane from that of FIG. 5. FIG. 8 isa cross section in a different plane from that of FIG. 7. FIGS. 9 and 10are exploded oblique views of a sixth lens group unit 77 and a focuslens unit 75. FIG. 11 is a simplified cross section of a focus motor 64.

In this embodiment, a three-dimensionally perpendicular coordinatesystem is set with respect to the digital camera 1. The optical axis AZ(an example of the optical axis center line) of the optical system L(discussed below) coincides with the Z axis direction (an example of theoptical axis direction). The X axis direction coincides with thehorizontal direction when the digital camera 1 is in its portraitorientation, and the Y axis direction coincides with the verticaldirection when the digital camera 1 is in its landscape orientation. Inthe following description, “front” means on the subject side of thedigital camera 1 (the Z axis positive direction side), and “rear” meansthe opposite side from the subject side of the digital camera 1 (theuser side, or the Z axis direction negative side).

Interchangeable Lens Unit

As shown in FIG. 1, the interchangeable lens unit 2 has the opticalsystem L, a lens support mechanism 71 that supports the optical systemL, a focus adjusting unit 72, an aperture adjusting unit 73, a blurcorrection unit 74, and a lens microcomputer 40 (an example of the drivecontroller).

(1) Optical System

The optical system L is a zoom lens system for forming an optical imageof a subject, and is mainly made up of four lens groups. Morespecifically, as shown in FIGS. 5 to 8, the optical system L has a firstlens group G1 having a positive refractive power, a second lens group G2having a negative refractive power, a third lens group G3 having anegative refractive power, a fourth lens group G4 having a positiverefractive power (an example of the first lens element), a fifth lensgroup G5 having a negative refractive power (an example of the focuslens), and a sixth lens group G6 having a positive refractive power (anexample of the second lens element, and an example of a lens element).The first to sixth lens groups G1 to G6 are each constituted by a singlelens.

When zooming in from the wide angle end to the telephoto end, the firstto sixth lens groups G1 to G6 each move in the Z axis direction alongthe optical axis AZ toward the subject side. An aperture unit 62 isdisposed between the third lens group G3 and the fourth lens group G4,and moves in the Z axis direction integrally with the third lens groupG3.

When focusing from an infinity focal state to a close focal state, thefifth lens group G5 moves along the optical axis AZ to the subject side.

Furthermore, the third lens group G3 moves in two directionsperpendicular to the optical axis AZ in order to suppress blurring inthe optical image attributable to movement of the digital camera 1.

(2) Lens Support Mechanism

The lens support mechanism 71 is for movably supporting the opticalsystem L, and has the lens mount 95, a fixed frame 50, a cam barrel 51,a first holder 52, a first lens group support frame 53, a second lensgroup support frame 54, a third lens group support frame 56, a fourthlens group support frame 57 (an example of the first lens supportframe), a fifth lens group support frame 58 (an example of the focuslens support frame), a sixth lens group support frame 59 (an example ofthe second lens support frame, and an example of a lens support frame),a zoom ring unit 83 (an example of the zoom mechanism), and a focus ringunit 88.

The lens mount 95 is the portion that is mounted to the body mount 4 ofthe camera body 3, and has a lens mount body 95 a, a lens mount contact91 (an example of the electrical contact), an electrical substrate 94,and a light blocking frame 60.

The lens mount body 95 a is fixed to the end of the fixed frame 50 onthe image plane side. The light blocking frame 60, the lens mountcontact 91, and the electrical substrate 94 are fixed to the lens mountbody 95 a. The light blocking frame 60 is a member that preventsunwanted light from being incident on an imaging sensor 11, and isdisposed on the inside of the lens mount body 95 a and on the imageplane side of the sixth lens group G6. The lens mount contact 91 and theelectrical substrate 94 will be discussed below.

The fixed frame 50 is a member that rotatably supports the cam barrel51, and is fixed to the lens mount body 95 a of the lens mount 95. Thefixed frame 50 has a protrusion 50 a at the end on the Z axis directionpositive side, three linear through-grooves 50 b disposed at an equalpitch around the optical axis AZ, and three linear through-grooves 50 cdisposed at an equal pitch around the optical axis AZ. In FIGS. 5 to 8,the linear through-grooves 50 b and 50 c are drawn so as to be arrangedwithin the same cross section.

The cam barrel 51 has a concave portion 51 a provided to the innerperiphery, three first cam grooves 51 b, three second cam grooves 51 c,three third cam grooves 51 d, three fourth cam grooves 51 e, and threefifth cam grooves 51 f. Since the protrusion 50 a of the fixed frame 50is inserted into the concave portion 51 a of the cam barrel 51, in astate in which relative movement is restricted in the Z axis direction,the cam barrel 51 is supported by the fixed frame 50 so as to berotatable with respect to the fixed frame 50.

The first lens group support frame 53 is fixed to the first holder 52and supports the first lens group G1. The first holder 52 has three campins 52 a that are disposed at an equal pitch in the circumferentialdirection. Since the cam pins 52 a are inserted into the linearthrough-grooves 50 b, the first holder 52 is able to move straight inthe Z axis direction with respect to the fixed frame 50, although itsrotation around the optical axis AZ is restricted with respect to thefixed frame 50. Furthermore, since the cam pins 52 a are inserted intothe first cam grooves 51 b of the cam barrel 51, when the cam barrel 51rotates around the optical axis AZ with respect to the fixed frame 50,the cam pins 52 a are guided by the first cam grooves 51 b, and thefirst holder 52 moves straight in the Z axis direction, without rotatingwith respect to the fixed frame 50. Female threads 52 c for attaching aconversion lens and an optical filter, such as a polarizing filter or aprotective filter, are formed at the distal end of the first holder 52.

The second lens group support frame 54 supports the second lens group G2and has three cam pins 54 a disposed at an equal pitch in thecircumferential direction. The cam pins 54 a are inserted into thelinear through-grooves 50 c, so the second lens group support frame 54is able to move straight in the Z axis direction with respect to thefixed frame 50, although its rotation around the optical axis AZ isrestricted with respect to the fixed frame 50. Furthermore, since thecam pins 54 a are inserted into the second cam grooves 51 c, when thecam barrel 51 rotates around the optical axis AZ with respect to thefixed frame 50, the cam pins 54 a are guided by the second cam grooves51 c, and the second lens group support frame 54 moves straight in the Zaxis direction, without rotating with respect to the fixed frame 50.

The third lens group support frame 56 supports a correction lens supportframe 55 to which the third lens group G3 is fixed, so as to allowmovement perpendicular to the optical axis AZ, and has three cam pins 55a disposed at an equal pitch in the circumferential direction. Since thecam pins 55 a are inserted into the linear through-grooves 50 c, thethird lens group support frame 56 is able to move straight in the Z axisdirection with respect to the fixed frame 50, although its rotationaround the optical axis AZ is restricted with respect to the fixed frame50. Furthermore, since the cam pins 55 a are inserted into the third camgrooves 51 d of the cam barrel 51, when the cam barrel 51 rotates aroundthe optical axis AZ with respect to the fixed frame 50, the cam pins 54a are guided by the third cam grooves 51 d, and the third lens groupsupport frame 56 moves straight in the Z axis direction, withoutrotating with respect to the fixed frame 50.

The fourth lens group support frame 57 supports the fourth lens groupG4, and has three cam pins 57 a disposed at an equal pitch in thecircumferential direction. Since the cam pins 57 a are inserted into thelinear through-grooves 50 c, the fourth lens group support frame 57 isable to move straight in the Z axis direction with respect to the fixedframe 50, although its rotation around the optical axis AZ is restrictedwith respect to the fixed frame 50. Furthermore, since the cam pins 55 aare inserted into the fourth cam grooves 51 e of the cam barrel 51, whenthe cam barrel 51 rotates around the optical axis AZ with respect to thefixed frame 50, the cam pins 55 a are guided by the fourth cam grooves51 e, and a fourth lens group unit 78 moves straight in the Z axisdirection, without rotating with respect to the fixed frame 50.

As shown in FIGS. 5 to 8, the movement range of the fourth lens groupunit 78 using the imaging sensor 11 as a reference is a first movementrange F4. Out of this first movement range F4, the position of thefourth lens group unit 78 at the wide angle end is termed the firstposition F41, and the position of the fourth lens group unit 78 at thetelephoto end is termed the second position F42. The reference for thefirst position F41 and second position F42 is the face of the fourthlens group unit 78 on the image plane side (more precisely, the face ofthe fourth lens group G4 on the image plane side).

The sixth lens group support frame 59 supports the sixth lens group G6,and has three cam pins 59 a disposed at an equal pitch in thecircumferential direction. The sixth lens group G6 and the sixth lensgroup support frame 59 constitute a sixth lens group unit 77 (an exampleof the second lens unit). Since cam pins 76 are inserted into the linearthrough-grooves 50 c, the sixth lens group support frame 59 is able tomove straight in the Z axis direction with respect to the fixed frame50, although its rotation around the optical axis AZ is restricted withrespect to the fixed frame 50. Furthermore, since the cam pins 59 a areinserted into the fifth cam grooves 51 f of the cam barrel 51, when thecam barrel 51 rotates around the optical axis AZ with respect to thefixed frame 50, the cam pins 59 a are guided by the fifth cam grooves 51f, and the sixth lens group unit 77 moves straight in the Z axisdirection, without rotating with respect to the fixed frame 50. Thesixth lens group unit 77 is disposed on the side nearest to the imageplane of the optical system L (the Z axis direction negative side).Therefore, when the interchangeable lens unit 2 is removed from thecamera body 3, the sixth lens group G6 can be seen from the lens mount95.

The fifth lens group support frame 58 supports the fifth lens group G5,and has a bearing part 58 a, an anti-rotation part 58 b, a rack support58 c, and a protrusion 58 d. The fifth lens group G5 and the fifth lensgroup support frame 58 constitute a focus lens unit 75. The focus lensunit 75 is disposed on the image plane side in the optical system L, andis disposed on the subject side of the sixth lens group unit 77.Accordingly, when the interchangeable lens unit 2 is removed from thecamera body 3, it is almost impossible to see the focus lens unit 75from the lens mount 95, so the user cannot touch the focus lens unit 75.

The sixth lens group support frame 59 supports the rear ends of twoguide poles 63 a and 63 b that extend in the Z axis direction. A firstguide pole support plate 65 a is a member for supporting the front endof the guide pole 63 a, and is fixed on the subject side of the sixthlens group support frame 59. A second guide pole support frame 65 b is amember for supporting the front end of the guide pole 63 b, and is fixedon the subject side of the sixth lens group support frame 59. The 63 aguide pole is inserted in the bearing part 58 a, and the guide pole 63 bis inserted in the anti-rotation part 58 b. The fifth lens group supportframe 58 is supported by the guide poles 63 a and 63 b movably in the Zaxis direction in a state in which rotation around the optical axis AZis restricted.

The rack support 58 c is disposed on the Z axis direction positive sideof the bearing part 58 a, and supports a rack 66 rotatably and movablyintegrally in the axial direction. The rack 66 has a plurality of teeth(not shown) that mesh with a lead screw 64 b (discussed below) of thefocus motor 64. The rotary motion of the lead screw 64 b is convertedinto linear motion in the Z axis direction by the rack 66.

A torsion coil spring 68 is attached to the rack support 58 c. Thetorsion coil spring 68 imparts rotational force around the rotationalaxis R2 (the A direction in FIG. 10) to the rack 66. This rotationalforce presses the rack 66 against the lead screw 64 b. This reducesbacklash between the rack 66 and the lead screw 64 b, and increases thepositional accuracy of the focus lens unit 75. Also, since the rack 66is constantly pressed against the lead screw 64 b, drive force can bemore efficiently transmitted from the lead screw 64 b to the rack 66.

The torsion coil spring 68 is also compressed in the Z axis direction(the direction parallel to the rotational axis R2) between the racksupport 58 c and the rack 66. The torsion coil spring 68 imparts apressing force F to the rack 66 (see FIG. 10), and the torsion coilspring 68 presses the rack 66 against the rack support 58 c in the Zaxis direction. This reduces movement of the rack 66 in the Z axisdirection with respect to the rack support 58 c, and further improvesthe positional accuracy of the focus lens unit 75.

The protrusion 56 d is a portion for detecting the starting point of thefocus lens unit 75, and is provided at a location that can pass throughthe detection region of a photosensor 67 (discussed below). In thisembodiment, since the fifth lens group G5 (a focus lens group) isconstituted by a single lens, the weight of the fifth lens group G5 canbe 1 g or less, for example, which allows the drive speed of the focusmotor 64 to be higher.

As shown in FIGS. 5 to 8, the movement range of the fourth lens groupunit 78 using the imaging sensor 11 as a reference is a second movementrange F5. Out of this second movement range F5, the position of thefocus lens unit 75 at the wide angle end is termed the first positionF51, and the position of the focus lens unit 75 at the telephoto end istermed the second position F52. The reference for the first position F51and second position F52 is the face of the focus lens unit 75 on thesubject side (more precisely, the face of the fifth lens group G5 on thesubject side). The first position F51 and second position F52 are thepositions of the focus lens unit 75 when the focus lens unit 75 isdriven on the basis of an infinity tracking table 100 (discussed below).

As shown in FIGS. 7 and 8, the second movement range F5 overlaps theabove-mentioned first movement range F4. The first position F41 isdisposed between the first position F51 and the second position F52. Thesecond position F52 is disposed between the first position F41 and thesecond position F42.

The zoom ring unit 83 has a ring base 86, the zoom ring 84 (an exampleof the zoom operating unit), and a linear position sensor 87 thatdetects the rotational position of the zoom ring 84. The “rotationalposition of the zoom ring 84” refers to the position of the zoom ring 84in the rotational direction, and can also be considered to be therotational angle of the zoom ring 84 from a reference position.

The zoom ring 84 has a cylindrical shape, and is supported by the ringbase 86 fixed to the fixed frame 50, so as to be movable around theoptical axis AZ in a state in which movement in the Z axis direction isrestricted. The zoom ring 84 has a through-hole 84 a at the end on the Zaxis direction negative side. A zoom drive pin 85 that is fixed to thecam barrel 51 is inserted into the through-hole 84 a. Consequently, thecam barrel 51 rotates integrally with the zoom ring 84 around theoptical axis AZ.

The linear position sensor 87 detects the rotational position androtational direction in which the user has put the zoom ring 84, andsends the detection result to the lens microcomputer 40. Morespecifically, the linear position sensor 87 is fixed to the ring base 86and has a slider 87 a that protrudes outward in the radial direction.This slider 87 a is inserted into a cam groove 84 b formed in the zoomring 84. When the zoom ring 84 is rotated with respect to the fixedframe 50, the slider 87 a moves in the Z axis direction along the camgroove 84 b. The linear position sensor 87 has a varistor, and when theslider 87 a sliders over a magnetic resistor that is inside thisvaristor, output (output voltage) that is proportional to the positionof the slider 87 a in the Z axis direction can be obtained linearlybetween terminals at both ends to which a specific voltage has beenapplied. The output of the linear position sensor 87 is converted intorotational position information, which allows the rotational position ofthe zoom ring 84 to be detected. The focal length of the optical systemL is displayed on the outer peripheral face of the zoom ring 84.

Since the first to sixth lens groups G1 to G6 are mechanically linkedvia the lens support mechanism 71, the absolute positions of the firstto sixth lens groups G1 to G6 (for example, positions using as areference the light receiving face 11 a of the imaging sensor 11) have aconstant relationship to the rotational position of the zoom ring 84.Therefore, the absolute positions of the first to sixth lens groups G1to G6 with respect to the lens mount 95, for example, can be ascertainedby detecting the rotational position of the zoom ring 84. The zoom ring84 may have another structure instead, such as a movable lever.

The focus ring unit 88 has a focus ring 89 and a focus ring angledetector 90 that detects the rotational angle of the focus ring 89. Thefocus ring 89 has a cylindrical shape, and is supported by the ring base81 rotatably around the optical axis AZ in a state in which movement inthe Z axis direction is restricted. The rotational angle and rotationaldirection of the focus ring 89 can be detected by the focus ring angledetector 90. The focus ring angle detector 90 has two photosensors 90 a,for example. The focus ring 89 has a plurality of protrusions 89 a thatprotrude inward in the radial direction and are disposed equidistantlyspaced in the rotational direction. Each of these photosensors has alight emitting part (not shown) and a light receiving part (not shown),and the plurality of protrusions 89 a pass in between the light emittingparts and the light receiving parts, allowing the rotational angle androtational direction of the focus ring 89 to be detected. The focus ring89 may have another structure instead, such as a movable lever.

(3) Focus Adjusting Unit

The focus adjusting unit 72 has the focus motor 64 (an example of afocus actuator, and an example of an actuator), a focus drive controller41, and the photosensor 67 (an example of a home position detector). Thefocus motor 64 is fixed to the sixth lens group unit 77 (more precisely,the sixth lens group support frame 59) and drives the focus lens unit 75in the Z axis direction with respect to the sixth lens group unit 77.The drive of the focus lens unit 75 with respect to the sixth lens groupunit 77 is performed by the focus motor 64 alone. In other words, in astate in which the focus motor 64 is not driving the focus lens unit 75(such as when no power is being supplied to the focus motor 64), thefocus lens unit 75 cannot be moved with respect to the sixth lens groupunit 77. In this case, the focus lens unit 75 moves in the Z axisdirection integrally with the sixth lens group unit 77.

The focus motor 64 is a stepping motor equipped with an encoder, and isfixed to the sixth lens group support frame 59 of the sixth lens groupunit 77. More specifically, as shown in FIG. 11, the focus motor 64 hasa stepping motor 64 d and an encoder 64 e (an example of a detector).

The stepping motor 64 d has a motor body 64 s (an example of an actuatorbody) and a drive shaft 64 a that protrudes from the motor body 64 s onthe Z axis direction positive side (subject side). We can also say thatthe motor body 64 s is provided to the end of the drive shaft 64 a onthe Z axis direction negative side (image plane side). The motor body 64s has a stator, and is disposed on the outer peripheral side of thesixth lens group G6. The lead screw 64 b is integrally formed on thedrive shaft 64 a. The lead screw 64 b is disposed on the Z axisdirection positive side of the motor body 64 s, and meshes with the rack66.

A motor holder 64 m is fixed to the stepping motor 64 d. The motorholder 64 m has a holder body 64 c and a distal end receiver 64 h. Theholder body 64 c is a rectangular plate that extends parallel to therotational axis R1 of the drive shaft 64 a. The distal end receiver 64 his integrally formed with the holder body 64 c, and rotatably supportsthe end of the drive shaft 64 a. The drive shaft 64 a is supported inthe thrust direction (a direction parallel to the rotational axis R1) bythe distal end receiver 64 h and a leaf spring 64 i. The drive shaft 64a is supported in the radial direction by the distal end receiver 64 hand a bearing 64 j.

The encoder 64 e is a unit for detecting the rotation of the drive shaft64 a, and is provided to the end of the stepping motor 64 d. The encoder64 e is disposed on the outer peripheral side of the sixth lens groupG6, and has a sensor magnet 64 f and a magnetic sensor 64 g. The encoder64 e is protected by a sensor protecting cover 64 k fixed to thestepping motor 64 d.

The sensor magnet 64 f is a cylindrical member that is fixed to theouter peripheral part of the drive shaft 64 a. N and S poles arealternately magnetized in the peripheral direction on the outerperipheral part of the sensor magnet 64 f. The magnetic sensor 64 g,which is used for angle detection, is disposed on the outer peripheralside of the sensor magnet 64 f so as to be opposite the sensor magnet 64f in the radial direction.

The magnetic sensor 64 g is a two-phase magnetoresistance effect type ofsensor, and is constituted by MR elements having a ferromagnetic thinfilm. These MR elements are provided in the drive direction at a spacingthat is one-quarter the magnetization pitch, from the N pole to the Spole of the sensor magnet 64 f. The magnetic sensor 64 g is disposedwith respect to the sensor magnet 64 f in a direction in which theorientation of the current flowing to the MR elements is perpendicularto the magnetization direction of the sensor magnet 64 f.

If we let the voltage applied to the magnetic sensor 64 g be an outputsignal, this output signal becomes two sinusoidal waveforms whose phasesdiffer by 90° (such as about 100 wavelengths per rotation). Thedetection resolution can be improved by subjecting these two signalwaveforms to modulated interpolation with a signal processing circuit(not shown) in the lens microcomputer 40.

The lens microcomputer 40 calculates electrical phase information andangle information about the drive shaft 64 a on the basis of the countvalues for electrical phase and angle processed by the signal processingcircuit. The lens microcomputer 40 calculates a drive command value fromthe computed angle information and electrical phase information. Thefocus drive controller 41 sends drive current to the focus motor 64according to this drive command value, thereby controlling the drive ofthe focus motor 64.

Thus, the rotational angle and torque of the drive shaft 64 a can becontrolled, and faster response, lower power consumption, and quieteroperation can be achieved by using an encoder-equipped stepping motor asthe focus motor 64 to perform closed loop control.

Furthermore, since the rotational angle of the drive shaft 64 a isalways being managed by the encoder 64 e, there is no step-out, whichcan be a problem with conventional stepping motors. Thus, employing anencoder-equipped stepping motor as the focus motor 64 makes it possibleto increase the speed to over 3000 pps, which is about four times the800 pps of an ordinary stepping motor.

As to the counting of the number of drive pulses mentioned above, whenan encoder-equipped stepping motor is used as the focus motor 64, theoutput value of the magnetic sensor 64 g may also be counted.

The rotary motion of the drive shaft 64 a generated by the focus motor64 is converted into linear motion in the Z axis direction of the focuslens unit 75 by the rack 66. Consequently, the focus lens unit 75 isable to move in the Z axis direction with respect to the sixth lensgroup unit 77.

With this digital camera 1, in order to realize a zoom lens system withwhich the subject distance is kept substantially constant while thefocal length can be varied, the focus lens unit 75 is driven by thefocus adjusting unit 72 on the basis of a tracking table that has beenstored in the lens microcomputer 40. This tracking system will be calledelectronic tracking here.

The tracking table is information indicating the position of the focuslens unit 75 at which the subject distance at which the subject is infocus even if the focal length changes is held substantially constant(more precisely, the position of the focus lens unit 75 with respect tothe sixth lens group unit 77). Saying that the subject distance issubstantially constant means that the amount of change in the subjectdistance is within a specific subject field depth. Electronic trackingwill be discussed below.

A photosensor 67, which detects the starting point position of the focuslens unit 75, is installed in the sixth lens group unit 77. Thisphotosensor 67 has a light emitting part (not shown) and a lightreceiving part (not shown). When the protrusion 56 d of the third lensgroup support frame 56 passes between the light emitting part and thelight receiving part, the photosensor 67 can detect the presence of theprotrusion 56 d. That is, the starting point position of the focus lensunit 75 with respect to the sixth lens group unit 77 can be detected bythe photosensor 67. In other words, the photosensor 67 is a startingpoint detector that detects the starting point position of the thirdlens group G3 with respect to the second lens group G2. The lensmicrocomputer 40 drives the third lens group G3 to the starting pointposition, and checks whether the focus lens unit 75 (the third lensgroup G3) is in the starting point position by using a signal from thephotosensor 67.

The starting point position that can be detected by the photosensor 67is an absolute position that never moves with respect to the sixth lensgroup unit 77. Accordingly, when the position of the focus lens unit 75is reset to the starting point position with respect to the sixth lensgroup unit 77, the focus lens unit 75 is driven to the position wherethe protrusion 56 d for starting point detection is detected by thephotosensor 67. For example, when a power switch 25 of the digitalcamera 1 is turned off, the focus motor 64 drives the focus lens unit 75to the position where the protrusion 56 d of the third lens groupsupport frame 56 is detected by the photosensor 67, regardless of thecurrent position of the focus lens unit 75. Upon completion of the driveof the focus lens unit 75, the power to the digital camera 1 is turnedoff. Conversely, when the power switch 25 of the digital camera 1 isturned on, the focus motor 64 drives the focus lens unit 75 to aspecific position determined on the basis of the tracking table. Thestarting point detector is not limited to being a photosensor, and mayinstead be a combination of a magnet and a magnetic sensor, for example.

(4) Aperture Adjusting Unit

The aperture adjusting unit 73 has the aperture unit 62 fixed to thethird lens group support frame 56, an aperture drive motor (not shown)that drives the aperture unit 62, and an aperture drive controller 42that controls the aperture drive motor. The aperture drive motor is astepping motor, for example. The aperture drive motor is driven on thebasis of a drive signal inputted from the aperture drive controller 42.The drive force generated by the aperture drive motor drives apertureblades 62 a in the opening and closing directions. The aperture value ofthe optical system L can be changed by driving the aperture blades 62 a.

(5) Blur Correction Unit

The blur correction unit 74 is for reducing blurring of the opticalimage attributable to movement of the interchangeable lens unit 2 andthe camera body 3, and has an electromagnetic actuator 46, a positiondetecting sensor 47, and a blur correction microcomputer 48.

The electromagnetic actuator 46 drives the correction lens support frame55 in a direction perpendicular to the optical axis AZ. Morespecifically, the electromagnetic actuator 46 has a magnet (not shown)and a coil (not shown), for example. For instance, the coil is providedto the correction lens support frame 55, and the magnet is fixed to thethird lens group support frame 56.

The position detecting sensor 47 is for detecting the position of thecorrection lens support frame 55 with respect to the third lens groupsupport frame 56, and is a Hall element, for example. A movementdetecting sensor (not shown) such as a gyro sensor is installed in theinterchangeable lens unit 2. The blur correction microcomputer 48controls the electromagnetic actuator 46 on the basis of the detectionresult of the position detecting sensor 47 and the detection result ofthe movement detecting sensor. Consequently, blurring of the opticalimage attributable to movement of the digital camera 1 can be reduced.

Reducing blurring of the subject image may instead be accomplished byelectronic blur correction, in which blurring that appears in an imageis corrected on the basis of image data outputted from the imagingsensor 11. Also, blurring of the optical image may be reduced by asensor shift method in which the imaging sensor 11 is driven in twodirections perpendicular to the optical axis AZ.

(6) Lens Microcomputer

The lens microcomputer 40 has a CPU (not shown), a ROM (not shown), anda memory 40 a, and various functions can be performed by readingprograms stored in the ROM into the CPU. For instance, the lensmicrocomputer 40 can check whether the focus lens unit 75 is in thestarting point position by using a detection signal from the photosensor67.

The memory 40 a is a nonvolatile memory, and can hold stored informationeven when no power is being supplied. The memory 40 a contains atracking table (discussed below) for realizing a zoom lens system, orinformation related to the interchangeable lens unit 2 (lensinformation), for example. The lens microcomputer 40 controls the focusmotor 64, and the focus lens unit 75 is driven by the focus motor 64 inthe Z axis direction, on the basis of this tracking table. An operationin which the position of the focus lens unit 75 is made to conform tochanges in the focal length on the basis of a tracking table willhereinafter be referred to as electronic tracking.

The lens microcomputer 40 has a counter 40 b for counting the number ofpulses of the focus motor 64. The counter 40 b is set to a count of “+1”when the focus lens unit 75 is driven to the Z axis direction positiveside, and to a count of “−1” when the focus lens unit 75 is driven tothe Z axis direction negative side. The lens microcomputer 40 canascertain the relative position of the third lens group G3 with respectto the second lens group G2 (the position of the focus lens unit 75 withrespect to the sixth lens group unit 77) by thus counting the number ofdrive pulses of the focus motor 64 by the counter 40 b.

For example, the rack 66 is driven by 0.3 mm in the Z axis direction forevery rotation of the lead screw 64 b of the focus motor 64. If thefocus motor 64, which has a 10-pole magnet (not shown), is driven by 1-2phase excitation, then the rack 66 is driven in the Z axis direction by0.3/20/2=0.0075 mm (7.5 μm) per pulse. During micro-step drive, the rack66 can be driven in even finer units. Using a stepping motor allows thefocus lens unit 75 to be driven in fine units, and reduces backlashduring reverse drive, for example. That is, selecting a stepping motoras the focus motor 64 affords very precise focus adjustment. Also,counting the number of drive pulses allows the current position of thefocus lens unit 75 with respect to the sixth lens group unit 77 to beascertained, and allows the amount of drive of the focus lens unit 75 tobe calculated.

Camera Body

The basic configuration of the camera body 3 will be described throughreference to FIGS. 1 to 4B. As shown in FIGS. 1 to 4B, the camera body 3has a case 3 a, a body mount 4, a control unit 39, an image acquisitionunit 35, an image display unit 36, a viewfinder unit 38, a bodymicrocomputer 10, and a battery 22.

(1) Case

The case 3 a constitutes the outer part of the camera body 3. As shownin FIGS. 4A and 4B, the body mount 4 is provided to the front face ofthe case 3 a, and the control unit 39 is provided to the rear and topfaces of the case 3 a. More specifically, a display unit 20, the powerswitch 25, a mode selector dial 26, a navigation key 27, a menu settingbutton 28, a setting button 29, a mode selector button 34, and a movingpicture capture operation button 24 are provided to the rear face of thecase 3 a. A shutter button 30 is provided to the top face of the case 3a.

(2) Body Mount

The body mount 4 is the portion where the lens mount 95 of theinterchangeable lens unit 2 is mounted, and has a body-side contact (notshown) that can be electrically connected with the lens mount contact91. The camera body 3 is able to send and receive data to and from theinterchangeable lens unit 2 via the body mount 4 and the lens mount 95.For example, the body microcomputer 10 (discussed below) sends the lensmicrocomputer 40 a control signal, such as an exposure synchronizationsignal, via the body mount 4 and the lens mount 95.

(3) Control Unit

As shown in FIGS. 4A and 4B, the operating unit 39 has various controlsthat the user can use to input operating information. For instance, thepower switch 25 is a switch for turning the power on and off to thedigital camera 1 or the camera body 3. When the power is turned on withthe power switch 25, power is supplied to the various parts of thecamera body 3 and the interchangeable lens unit 2.

The mode selector dial 26 is used to switch the operating mode, such asstill picture capture mode, moving picture capture mode, or reproductionmode, and the user can turn the mode selector dial 26 to switch theoperating mode. When the still picture capture mode is selected with themode selector dial 26, the operating mode is switched to the stillpicture capture mode, and when the moving picture capture mode isselected with the mode selector dial 26, the operating mode is switchedto the moving picture capture mode. In the moving picture capture mode,basically moving picture capture is possible. When the reproduction modeis selected with the mode selector dial 26, the operating mode isswitched to the reproduction mode, allowing the captured image to bedisplayed on the display unit 20.

The navigation key 27 is used to select the left, right, up, and downdirections. The user can use the navigation key 27 to select the desiredmenu from various menu screens displayed on the display unit 20, forexample.

The menu setting button 28 is for setting the various operations of thedigital camera 1. The setting button 29 is for executing the operationsof the various menus.

The moving picture capture operation button 24 is for starting andstopping the capture of moving pictures. Even if the operating modeselected with the mode selector dial 26 is the still picture capturemode or the reproduction mode, when the moving picture capture operationbutton 24 is pressed, the operating mode is forcibly changed to themoving picture capture mode, and moving picture capture begins,regardless of the setting on the mode selector dial 26. When this movingpicture capture operation button 24 is pressed during the capture of amoving picture, the moving picture capture ends and the operating modechanges to the one selected on the mode selector dial 26, that is, tothe one prior to the start of moving picture capture. For example, ifthe still picture capture mode has been selected with the mode selectordial 26 when the moving picture capture operation button 24 is pressed,the operating mode automatically changes to the still picture capturemode after the moving picture capture operation button 24 is pressedagain.

The shutter button 30 is pressed by the user to capture an image. Whenthe shutter button 30 is pressed, a timing signal is outputted to thebody microcomputer 10. The shutter button 30 is a two-stage switch thatcan be pressed half way down or all the way down. Light measurement andranging are commenced when the user presses the button half way down.When the user presses the shutter button 30 all the way down in a statein which the shutter button 30 has been pressed half way down, a timingsignal is outputted, and image data is acquired by the image acquisitionunit 35.

As shown in FIG. 2, a lens attachment button 99 (an example of the lensattachment operating unit) for attaching and removing theinterchangeable lens unit 2 to and from the camera body 3 is provided tothe front face of the camera body 3. The lens attachment button 99 has acontact (not shown) that is in its “on” state when the button is pressedby the user, for example, and is electrically connected to the bodymicrocomputer 10. When the lens attachment button 99 is pressed, thebuilt-in contact is switched on, and the body microcomputer 10recognizes that the lens attachment button 99 has been pressed.

(4) Image Acquisition Unit

The image acquisition unit 35 mainly comprises the imaging sensor 11 (anexample of the imaging element) such as a CCD (Charge Coupled Device)that performs opto-electrical conversion, a shutter unit 33 that adjuststhe exposure state of the imaging sensor 11, a shutter controller 31that controls the drive of the shutter unit 33 on the basis of a controlsignal from the body microcomputer 10, and an imaging sensor drivecontroller 12 that controls the operation of the imaging sensor 11.

The imaging sensor 11 is a CCD (Charge Coupled Device) sensor, forexample, that converts the optical image formed by the optical system Linto an electrical signal. The imaging sensor 11 is driven andcontrolled on the basis of timing signals generated by the imagingsensor drive controller 12. The imaging sensor 11 may instead be a CMOS(Complementary Metal Oxide Semiconductor) sensor.

The shutter controller 31 drives a shutter drive actuator 32 andoperates the shutter unit 33 according to a control signal outputtedfrom the body microcomputer 10 that has received a timing signal.

The auto-focusing method that is employed in this embodiment is acontrast detection method that makes use of image data produced by theimaging sensor 11. Using a contrast detection method allowshigh-precision focal adjustment.

(5) Body Microcomputer

The body microcomputer 10 is a control device that is the command centerof the camera body 3, and controls the various components of the digitalcamera 1 according to operation information inputted to the operationunit 39. More specifically, the body microcomputer 10 is equipped with aCPU, ROM, and RAM, and the programs held in the ROM are read by the CPU,allowing the body microcomputer 10 to perform a variety of functions.For instance, the body microcomputer 10 has the function of detectingthat the interchangeable lens unit 2 has been mounted to the camera body3, or the function of acquiring information about controlling thedigital camera 1, such as information about the focal length from theinterchangeable lens unit 2.

The body microcomputer 10 is able to receive signals from the powerswitch 25, the shutter button 30, the mode selector dial 26, thenavigation key 27, the menu setting button 28, and the setting button29. Various information related to the camera body 3 is held in a memory10 a inside the body microcomputer 10. The memory 10 a is a nonvolatilememory, and can hold stored information even when no power is beingsupplied.

Also, the body microcomputer 10 periodically produces a verticalsynchronization signal, and produces an exposure synchronization signalon the basis of the vertical synchronization signal in parallel with theproduction of the vertical synchronization signal. The bodymicrocomputer 10 can produce an exposure synchronization signal, sincethe body microcomputer 10 ascertains beforehand the exposure starttiming and the exposure stop timing based on the verticalsynchronization signal. The body microcomputer 10 outputs a verticalsynchronization signal to a timing generator (not shown), and outputs anexposure synchronization signal at a specific period to the lensmicrocomputer 40 via the body mount 4 and the lens mount 95. The lensmicrocomputer 40 acquires position information about the focus lens unit75.

The imaging sensor drive controller 12 produces an electronic shutterdrive signal and a read signal of the imaging sensor 11 at a specificperiod on the basis of the vertical synchronization signal. The imagingsensor drive controller 12 drives the imaging sensor 11 on the basis ofthe electronic shutter drive signal and the read signal. That is, theimaging sensor 11 reads to a vertical transfer part (not shown) theimage data produced by numerous opto-electrical conversion element (notshown) present in the imaging sensor 11, according to the read signal.

The body microcomputer 10 also controls the focus adjusting unit 72(discussed below) via the lens microcomputer 40.

The image signal outputted from the imaging sensor 11 is sent from ananalog signal processor 13 and successively processed by an A/Dconverter 14, a digital signal processor 15, a buffer memory 16, and animage compressor 17. The analog signal processor 13 subjects the imagesignal outputted from the imaging sensor 11 to gamma processing or othersuch analog signal processing. The A/D converter 14 converts the analogsignal outputted from the analog signal processor 13 into a digitalsignal. The digital signal processor 15 subjects the image signalconverted into a digital signal by the A/D converter 14 to digitalsignal processing such as noise elimination or contour enhancement. Thebuffer memory 16 is a RAM (Random Access Memory), and temporarily storesthe image signal. The image signal stored in the buffer memory 16 issent to and processed by first the image compressor 17 and then an imagerecorder 18. The image signal stored in the buffer memory 16 is read ata command from an image recording controller 19 and sent to the imagecompressor 17. The data of the image signal sent to the image compressor17 is compressed into an image signal according to a command from theimage recording controller 19. This compression adjusts the image signalto a smaller data size than that of the original data. An example of themethod for compressing the image signal is the JPEG (Joint PhotographicExperts Group) method in which compression is performed on the imagesignal for each frame. After this, the compressed image signal isrecorded by the image recording controller 19 to the image recorder 18.When a moving picture is recorded, JEPG was used to compress a pluralityof image signals, compressing an image signal for each frame, and anH.264/AVC method can also be used, in which compression is performed onimage signals for a plurality of frames all at once.

The image recorder 18 produces a still picture file or moving picturefile that is associated with specific information to be recorded withthe image signal. The image recorder 18 also records the still picturefile or moving picture file on the basis of a command from the imagerecording controller 19. The image recorder 18 is a removable memoryand/or an internal memory, for example. The specific information to berecorded with the image signal includes the date the image was captured,focal length information, shutter speed information, aperture valueinformation, and photography mode information. Still picture files arein Exif (TRADEMARK) format or a format similar to Exif (TRADEMARK)format. Moving picture files are in H.264/AVC format or a format similarto H.264/AVC format.

(6) Image Display Unit

The image display unit 36 has the display unit 20 and an image displaycontroller 21. The display unit 20 is a liquid crystal monitor, forexample. The display unit 20 displays as a visible image the imagesignal recorded to the buffer memory 16 or the image recorder 18 on thebasis of a command from the image display controller 21. Possibledisplay modes on the display unit 20 include a display mode in whichonly the image signal is displayed as a visible image, and a displaymode in which the image signal and information from the time of captureare displayed as a visible image.

(7) Viewfinder

The viewfinder unit 38 has a liquid crystal viewfinder 8 that displaysthe image acquired by the imaging sensor 11, and a viewfinder eyepiecewindow 9 provided to the rear face of the case 3 a. The user looks intothe viewfinder eyepiece window 9 to view the image displayed on theliquid crystal viewfinder 8.

(8) Battery

The battery 22 supplies power to the various components of the camerabody 3, and also supplies power to the interchangeable lens unit 2 viathe lens mount 95. In this embodiment, the battery 22 is a rechargeablebattery. The battery 22 may be a dry cell, or may be an external powersupply, with which power is supplied from the outside through a powercord.

Tracking Table

With the digital camera 1, electronic tracking is performed by the focusadjusting unit 72 so that the focal length can be varied while thesubject distance is kept substantially constant. More specifically, asshown in FIG. 12, to perform electronic tracking, tracking informationincluding a tracking table 100 is held in the memory 40 a. This trackingtable 100 shows the relationship between the rotational position of thezoom ring 84 and the position of the focus lens unit 75 in the Z axisdirection with respect to the sixth lens group unit 77. For example, thememory 40 a holds three tracking tables 100 corresponding to subjectdistances of 0.3 m, 1.0 m, and infinity (∞).

The tracking table 100 consists of discrete information in which therotational position of the zoom ring 84 and the position of the focuslens unit 75 in the Z axis direction are divided into several groups. Ingeneral, the number of divisions is determined so that the subjectdistance will fit within a specific subject field depth even if the zoomring 84 is turned.

The rotational position of the zoom ring 84 (position in the rotationaldirection) can be detected by the linear position sensor 87. On thebasis of this detection result and the tracking table 100, the lensmicrocomputer 40 can determine the position of the focus lens unit 75 inthe Z axis direction with respect to the sixth lens group unit 77.

As shown in FIG. 12, each tracking table 100 is shown as a curve thatgently curves from the wide angle end to the telephoto end. While thestate of the optical system L is changing from the wide angle end to thetelephoto end, the focus lens unit 75 moves away from the sixth lensgroup unit 77.

This tracking table 100 does not have an inflection point between thewide angle end and the telephoto end. An inflection point is the pointat which the drive direction of the focus lens unit 75 changes while thezoom ring 84 is operated from the wide angle end to the telephoto end.That is, the lens microcomputer 40 controls the focus motor 64 so thatthe focus lens unit 75 is driven in one direction with respect to thesixth lens group unit 77 when the sixth lens group unit 77 is beingdriven by the zoom ring unit 83 in that direction with respect to theimaging sensor 11.

Also, the sixth lens group G6 (the sixth lens group unit 77) moves awayfrom the imaging sensor 11 (upward in FIG. 12) while the state of theoptical system L is changing from the wide angle end to the telephotoend. That is, in this embodiment, the movement direction of the sixthlens group unit 77 with respect to the imaging sensor 11 is the same asthe movement direction of the focus lens unit 75 with respect to thesixth lens group unit 77.

If the focus lens unit 75 is driven on the basis of the infinitytracking table 100 shown in FIG. 12, as the sixth lens group unit 77moves by a distance F in the Z axis direction with respect to theimaging sensor 11, the focus lens unit 75 moves by a distance G in the Zaxis direction with respect to the sixth lens group unit 77. As aresult, the focus lens unit 75 moves by a distance H, which is the sumof the distances G and F, in the Z axis direction with respect to theimaging sensor 11.

Thus, since the movement distance of the sixth lens group unit 77 isadded to the drive distance of the focus lens unit 75, a sufficientlylarge movement distance of the focus lens unit 75 with respect to theimaging sensor 11 can be ensured.

The starting point position D of the focus lens unit 75 with respect tothe sixth lens group unit 77 is detected by the photosensor 67, which isindicated by the one-dot chain line in FIG. 12. In this embodiment, thestarting point position D is located in the center of the third movementrange E of the focus lens unit 75 (between the first position E1 and thesecond position E2) in the infinity tracking table 100. The firstposition E1 is the position of the focus lens unit 75 corresponding tothe wide angle end in the infinity tracking table 100. The secondposition E2 is the position of the focus lens unit 75 corresponding tothe telephoto end in the infinity tracking table 100.

Thus disposing the starting point position D in the center allows thefocus lens unit 75 to be moved relatively quickly to any position whenthe power is turned on to the digital camera 1.

The reason the starting point position D is determined using theinfinity tracking table 100 as a reference is that there is a higherprobability of capturing the subject at the infinity position when theuser turns on the power to the digital camera 1 to photograph thesubject.

The tracking table 100 may also be expressed by a polynomial, ratherthan discrete information divided into several groups. Positioninformation about the first lens group G1, second lens group G2, orfourth lens group G4 in the Z axis direction may also be used instead ofthe rotational position of the zoom ring 84. The “position of the focuslens unit 75 in the Z axis direction with respect to the sixth lensgroup unit 77” can be rephrased as the position of the third lens groupG3 in the Z axis direction with respect to the sixth lens group unit 77,or the position of the third lens group G3 in the Z axis direction withrespect to the second lens group G2.

Detailed Configuration of Lens Mount

The lens mount 95 will be described in detail through reference to FIGS.13 and 14. FIG. 13 is a simplified oblique view of the area around thelens mount contact 91 and the electrical substrate 94 when viewed fromthe imaging sensor 11 side. FIG. 14 is a simplified plan view of thearea around the lens mount contact 91 and the electrical substrate 94when viewed from the imaging sensor 11 side. FIG. 13 shows the state atthe wide angle end, which corresponds to the state shown in FIGS. 5 and6, for example.

As discussed above, the lens mount 95 has the lens mount body 95 a, thelens mount contact 91 (an example of the electrical contact), theelectrical substrate 94, and the light blocking frame 60.

The lens mount contact 91 can be electrically connected to a body mountcontact (not shown) provided to the body mount 4, and has a plurality ofelectrical contacts 91 a (11 electrical contacts 91 a in thisembodiment), a contact support frame 91 b that supports the electricalcontacts 91 a, a flexible printed cable 96, and a connector 96 a.

The electrical contacts 91 a are disposed at an equal pitch in thedirection along an arc whose center is the optical axis AZ. The contactsupport frame 91 b is an arc-shaped member whose center is the opticalaxis AZ. The flexible printed cable 96 is connected to the electricalcontacts 91 a. The connector 96 a electrically connects the flexibleprinted cable 96 and the electrical substrate 94.

The electrical substrate 94 is disposed on the subject side of the lensmount body 95 a, and is fixed to the lens mount body 95 a. Electroniccomponents such as the lens microcomputer 40 are mounted to theelectrical substrate 94. The electrical substrate 94 is electricallyconnected to the lens mount contact 91 via the connector 96 a.

As shown in FIGS. 13 and 14, when viewed in the Z axis direction, thelens mount contact 91 is disposed on the opposite side from the focusmotor 64 with respect to the sixth lens group G6. More precisely, if welet the line that passes through the center C of the lens mount contact91 and is perpendicular to the optical axis AZ of the sixth lens groupG6 be a first imaginary line P, the focus motor 64 is disposed on theopposite side from the lens mount contact 91 with respect to a secondimaginary line M1 that is perpendicular to the first imaginary line Pand the optical axis AZ. That is, in FIGS. 13 and 14, the focus motor 64is disposed within the range M that is above the second imaginary lineM1.

Also, the focus motor 64 is disposed at a position that is symmetricalwith the lens mount contact 91 using the optical axis AZ of the sixthlens group G6 as a reference (more precisely, around the center C of thelens mount contact 91). More precisely, the contact support frame 91 bhas a first end 91 c and a second end 91 d. We will let the line that isperpendicular to the optical axis AZ and passes through the first end 91c be a third imaginary line N1, and let the line that is perpendicularto the optical axis AZ and passes through the second end 91 d be afourth imaginary line N2. When the focus motor 64 is said to be disposedat a position that is symmetrical with the lens mount contact 91 usingthe optical axis AZ as a reference, it means that when viewed in the Zaxis direction, the focus motor 64 is disposed within a range N betweenthe third imaginary line N1 and the fourth imaginary line N2.

The first imaginary line P overlaps the focus motor 64, and intersectsthe rotational axis R1 of the focus motor 64. That is, the rotationalaxis R1, the optical axis AZ, and the center C of the lens mount contact91 are all disposed on the same straight line when viewed in the Z axisdirection.

Since the lens mount contact 91 is thus disposed on the opposite sidefrom the focus motor 64 with respect to the sixth lens group G6, thefocus motor 64 can be disposed at a position away from the lens mountcontact 91. This means that the encoder 64 e of the focus motor 64 willbe less affected by noise generated by the lens mount contact 91, andthere will be less of a decrease in the detection accuracy of theencoder 64 e.

Also, the connector 96 a is disposed on the opposite side from the focusmotor 64 with respect to the sixth lens group G6 when viewed in the Zaxis direction. More precisely, the connector 96 a is disposed on theopposite side from the focus motor 64 with respect to the lens mountcontact 91. That is, the connector 96 a is disposed farther away fromthe focus motor 64 than the lens mount contact 91. Furthermore, whenviewed in the Z axis direction, the connector 96 a overlaps the firstimaginary line P. Consequently, the encoder 64 e is less likely to beaffected by noise generated by the connector 96 a.

Also, the electrical substrate 94 is disposed on the outer peripheralside of the sixth lens group G6 so as to surround the sixth lens groupG6, and has a cut-out 94 a at a position corresponding to the focusmotor 64. More precisely, the electrical substrate 94 is roughlyC-shaped, and has a first substrate end 94 b and a second substrate end94 c disposed to the sides of the focus motor 64. The cut-out 94 a isformed by the first substrate end 94 b and the second substrate end 94c.

Since the electrical substrate 94 is thus roughly C-shaped, rather thanbeing annular, even though the electrical substrate 94 is disposedwithin the range of movement of the focus motor 64 in the Z axisdirection, the focus motor 64 does not come into contact with theelectrical substrate 94. Accordingly, the interchangeable lens unit 2can be more compact.

Operation of the Digital Camera

The operation of the digital camera 1 will be described.

(1) Imaging Mode

This digital camera 1 has two imaging modes. More specifically, thedigital camera 1 has a viewfinder imaging mode in which the user looksthrough the viewfinder eyepiece window 9 to view the subject, and amonitor imaging mode in which the user observes the subject on thedisplay unit 20.

With the viewfinder imaging mode, the image display controller 21 drivesthe liquid crystal viewfinder 8, for example. As a result, an image ofthe subject (a so-called through-image) acquired by the imaging sensor11 is displayed on the liquid crystal viewfinder 8.

With the monitor imaging mode, the display unit 20 is driven by theimage display controller 21, for example, and a real-time image of thesubject is displayed on the display unit 20. Switching between these twoimaging modes can be performed with the mode selector button 34.

(2) Zoom Operation

Next, the operation of the interchangeable lens unit 2 when the userperforms zooming will be described.

When the user rotates the zoom ring 84, the cam barrel 51 rotates alongwith the zoom ring 84. When the cam barrel 51 rotates around the opticalaxis AZ, the first holder 52 is guided by the first cam grooves 51 b ofthe cam barrel 51, and moves linearly in the Z axis direction withrespect to the fixed frame 50. The second lens group support frame 54,the third lens group support frame 56, the fourth lens group unit 78,and the sixth lens group unit 77 are also guided by the second camgrooves 51 c, the third cam grooves 51 d, the fourth cam grooves 51 e,and the fifth cam grooves 51 f of the cam barrel 51, and move linearlyin the Z axis direction with respect to the fixed frame 50. Thus, byrotating the zoom ring 84, the state of the interchangeable lens unit 2can be changed from the wide angle end state shown in FIGS. 5 and 6 tothe telephoto end state shown in FIGS. 7 and 8. Consequently, thesubject can be imaged at the desired zoom position by adjusting therotational position of the zoom ring 84.

The sixth lens group unit 77 is mechanically driven in the Z axisdirection by rotating the zoom ring 84 here, but only the focus lensunit 75 is electrically driven and controlled by the focus adjustingunit 72 on the basis of the tracking table 100 stored ahead of time inthe memory 40 a, so that the subject distance remains substantiallyconstant. For example, when the focus lens unit 75 is driven by thefocus motor 64 on the basis of the tracking table 100, the focal statecan be kept at infinity both when the move is from the wide angle end tothe telephoto end, and when the move is from the telephoto end to thewide angle end.

More precisely, when the zoom ring 84 is turned, the first lens group G1to the sixth lens group G6 move in the Z axis direction along theoptical axis AZ. Consequently, the magnification of the subject imagechanges. At this point the focus lens unit 75 moves in the Z axisdirection along the optical axis AZ in a state of being supported by thesixth lens group unit 77. When there is a relative change in thepositional relationship of the first lens group G1 to the sixth lensgroup G6, the focal state of the subject image formed on the imagingsensor 11 also changes. That is, the subject distance at which the focalpoint is formed on the imaging sensor 11 changes.

In view of this, with the digital camera 1, even if the focal lengthchanges, the subject distance can be kept substantially constant bydriving the focus motor 64 according to the rotational position of thezoom ring 84. More specifically, using just the focus motor 64, thefocus lens unit 75 including the fifth lens group G5 is moved withrespect to the sixth lens group unit 77. The lens microcomputer 40acquires the current rotational position of the zoom ring 84 on thebasis of the detection signal of the linear position sensor 87. At thesame time, the lens microcomputer 40 calculates the position of thefocus lens unit 75 with respect to the sixth lens group unit 77 from thecount value at the counter 40 b. Utilizing the plurality of trackingtables 100 shown in FIG. 12, the lens microcomputer 40 finds the currentsubject distance from these two pieces of information (the currentrotational position of the zoom ring 84, and the position of the focuslens unit 75 with respect to the sixth lens group unit 77), and selectsthe tracking table 100 corresponding to the subject distance thus found.Here, we will assume that the tracking table 100 corresponding toinfinity was selected.

Next, the lens microcomputer 40 again acquires the rotational positionof the zoom ring 84, and finds the rotational speed of the zoom ring 84,that is, the rate of change in the focal length, from the amount ofchange in the rotational position of the zoom ring 84.

Next, the lens microcomputer 40 predicts the rotational position of thezoom ring 84 after the elapse of a specific time from the currentrotational angle of the zoom ring 84 and the rotational speed of thezoom ring 84, and finds as a target position the position of the focuslens unit 75 in the Z axis direction corresponding to the predictedrotational position of the zoom ring 84. After the elapse of a specifictime, the lens microcomputer 40 drives the focus motor 64 via the focusdrive controller 41 so that the focus lens unit 75 will be located atthis target position. Consequently, the focus lens unit 75 is driven soas to follow the movement of the other lens groups, and the subjectdistance is kept constant.

Thus, in the electronic tracking operation, the lens microcomputer 40predicts the change in the focal length that will accompany zoomingoperation, and acquires from the tracking table 100 the target positionof the focus lens unit 75 corresponding to the predicted focal length.The focus lens unit 75 is driven to the target position by the focusmotor 64 in parallel with the zooming operation of the optical system L.Since this operation is executed at specific time intervals, even if thezoom ring 84 is rotated and the focal length of the optical system Lchanges, the focus lens unit 75 will move to the Z axis directionposition corresponding to the focal length on the basis of the trackingtable 100, and the drive of the focus lens unit 75 can conform to thechange in the focal length. Consequently, the subject distance can bekept substantially constant regardless of any change in the focallength. The control of these components may be performed by the bodymicrocomputer 10, rather than lens microcomputer 40.

Similarly, when the focused subject distance is short, such as 1 m, forexample, the tracking table 100 for which the subject distance is 1 m isselected, and both when the move is from the wide angle end to thetelephoto end, and when the move is from the telephoto end to the wideangle end, the focused state at a short distance can be maintained bydriving the focus motor 64, and the zooming operation can be carried outsmoothly.

In particular, since the focus lens unit 75 and the focus motor 64 movein the Z axis direction integrally with the sixth lens group unit 77,even if the user turns the zoom ring 84 quickly, the focus lens unit 75can still be moved integrally with the sixth lens group unit 77.Therefore, if the subject distance is to be kept substantially constantbefore and after the zooming operation, the focus motor 64 may move thefifth lens group G5 by a distance obtained by subtracting the distancethat the sixth lens group G6 is moved by the cam mechanism with respectto the imaging sensor 11 from the distance that the fifth lens group G5is to be moved with respect to the imaging sensor 11. This makes it easyto keep up with fast operation of the zoom ring 84 by the user.

Also, in this embodiment, if a zooming operation is performed from thewide angle end to the telephoto end, with the subject distance atinfinity, the focus lens unit 75 (more precisely, the fifth lens groupG5, which is a focus lens group) must be moved in the Z axis directionby about 3 mm with respect to the imaging sensor 11. When the focusmotor 64 is driven at 3000 pps, the amount of drive of the focus lensunit 75 per rotation of the focus motor 64 is 0.3 mm as mentioned above,so it takes 0.4 second to move the focus lens unit 75 by 10 mm in the Zaxis direction on the basis of the tracking table. Since it is possibleto move the focus lens unit 75 from the wide angle end to the telephotoend in approximately 0.4 second, even if the user should turn the zoomring 84 from the wide angle end to the telephoto end in 0.5 second, thedrive of the focus lens unit 75 can keep up with the change in focallength. Consequently, even if the user should perform a quick zoomingoperation while looking at the subject on the display unit 20 in liveview mode, for example, the subject image that shows on the display unit20 will be unlikely to be blurred, and this makes the camera easier touse.

(3) Focusing Operation

Next, the focusing operation of the digital camera 1 will be described.The digital camera 1 has two focus modes: an auto-focus imaging mode anda manual imaging mode. The user of the digital camera 1 can select thefocus mode with a focus imaging mode setting button (not shown) providedto the camera body 3.

In the auto-focus imaging mode, auto-focus operation is performed bycontrast detection method. When auto-focusing is performed by contrastdetection method, the body microcomputer 10 asks the lens microcomputer40 for contrast AF data. This contrast AF data is necessary inauto-focusing by contrast detection method, and includes, for example,the focus drive speed, focus shift amount, image magnification ratio,and information about whether contrast AF is possible.

The body microcomputer 10 monitors whether or not the shutter button 30has been pressed half way down. If the shutter button 30 has beenpressed half way down, the body microcomputer 10 issues an auto-focuscommencement command to the lens microcomputer 40. This auto-focuscommencement command is to start the auto-focus operation by contrastdetection method. Upon receiving this command, the lens microcomputer 40drives and controls the focus motor 64, which is a focus actuator. Moreprecisely, the lens microcomputer 40 sends a control signal to the focusdrive controller 41. On the basis of this control signal, the focusdrive controller 41 drives the focus motor 64, and the focus lens unit75 moves minutely.

The body microcomputer 10 calculates an evaluation value for auto-focusoperation (hereinafter referred to as an AF evaluation value) on thebasis of the received image data. More specifically, the bodymicrocomputer 10 sends a command to the digital signal processor 15. Thedigital signal processor 15 sends an image signal to the bodymicrocomputer 10 at a specific timing on the basis of the receivedcommand. The body microcomputer 10 finds a brightness signal from theimage data produced by the imaging sensor 11, and finds the AFevaluation value by integrating the high-frequency component within thescreen of the brightness signal. The AF evaluation value thus calculatedis stored in a DRAM (not shown) in a state of being associated with theexposure synchronization signal. Since the lens position informationacquired by the body microcomputer 10 from the lens microcomputer 40 isalso associated with the exposure synchronization signal, the bodymicrocomputer 10 can store the AF evaluation value with it associatedwith the lens position information.

Next, the body microcomputer 10 extracts as the focal point the positionof the focus lens unit 75 where the AF evaluation value is at itsmaximum, on the basis of the AF evaluation value stored in the DRAM. Themethod for driving the focus lens unit 75 in the extraction of the focalpoint is generally known as a hill climbing method. With a hill climbingmethod, the focus lens unit 75 is moved in the direction of increasingthe AF evaluation value, and the AF evaluation value is found for eachposition of the focus lens unit 75. This operation is continued untilthe maximum value for the AF evaluation value is detected, that is,until the AF evaluation value increases up to its peak and begins todecrease.

The body microcomputer 10 sends a control signal to the focus drivecontroller 41 via the lens microcomputer 40 so that the focus lens unit75 will be driven to the position corresponding to the extracted focalpoint. The focus drive controller 41 produces a drive pulse for drivingthe focus motor 64 on the basis of a control signal from the bodymicrocomputer 10 (or the lens microcomputer 40), for example. The focusmotor 64 is driven by an amount corresponding to this drive signal, andthe focus lens unit 75 moves in the Z axis direction to the positioncorresponding to the focal point.

Focusing in auto-focus imaging mode is performed in this way with thedigital camera 1. The above operation is executed instantly when theuser presses the shutter button 30 half way down.

Focusing by contrast detection method can also be carried out in monitorimaging mode (known as viewfinder mode), in which real-time image datacan be produced with the imaging sensor 11. The reason for this is thatin viewfinder mode, image data is produced in a steady state by theimaging sensor 11, and auto-focusing by contrast detection method usingthis image data is easy.

In viewfinder mode, since a real-time image of the subject is displayedon the display unit 20, the user can decide on the composition fortaking the still picture or moving picture while looking at the displayunit 20. Also, there is another imaging mode the user can select inaddition to live view mode using the display unit 20, which is a secondlive view mode (viewfinder imaging mode) in which the subject image fromthe interchangeable lens unit 2 is guided to the liquid crystalviewfinder 8 (viewfinder unit 38).

The manual focus imaging mode will now be described.

When the user turns the focus ring 89, the focus ring angle detector 90detects the rotational angle of the focus ring 89 and outputs a signalcorresponding to this rotational angle. The focus drive controller 41 isable to receive signals from the focus ring angle detector 90, and ableto send signals to the focus motor 64. The focus drive controller 41sends the decision result to the lens microcomputer 40. The focus drivecontroller 41 drives the focus motor 64 on the basis of a control signalfrom the lens microcomputer 40. More precisely, the lens microcomputer40 produces a drive signal for driving the focus motor 64 on the basisof a focus ring rotational angle signal. When the lead screw 64 a of thefocus motor 64 rotates according to the drive signal, the focus lensunit 75 moves in the Z axis direction via the rack 66 that meshes withthe lead screw 64 a. In the wide angle end state shown in FIGS. 5 and 6,the subject distance is infinity, but as the subject distance drawscloser, the focus lens unit 75 moves to the Z axis direction negativeside. Similarly, in the telephoto end state shown in FIGS. 7 and 8, thesubject distance is infinity, but as the subject distance becomesshorter, the focus lens unit 75 moves to the Z axis direction negativeside. The amount of movement of the focus lens unit 75 is greater inthis case than in the case of the wide angle end.

In this way, the user can perform focusing by turning the focus ring 89while looking at the subject on the display unit 20. In the manual focusimaging mode, when the user presses the shutter button 30 all the waydown, imaging is performed in this unchanged state.

(4) Still Picture Capture

When the user presses the shutter button 30 all the way down, a commandis sent from the body microcomputer 10 to the lens microcomputer 40 sothat the aperture value of the optical system L will be set to theaperture value calculated on the basis of the light measurement outputof the imaging sensor 11. The aperture drive controller 42 is controlledby the lens microcomputer 40, and the aperture unit 62 is constricted tothe indicated aperture value. Simultaneously with the indication of theaperture value, a drive command is sent from the imaging sensor drivecontroller 12 to the imaging sensor 11, and a shutter unit 33 drivecommand is sent out. The imaging sensor 11 is exposed by the shutterunit 33 for a length of time corresponding to the shutter speedcalculated on the basis of the light measurement output of the imagingsensor 11.

The body microcomputer 10 executes imaging processing and, when theimaging is completed, sends a command signal to the image recordingcontroller 19. The image recorder 18 records an image signal to aninternal memory and/or removable memory on the basis of the command ofthe image recording controller 19. The image recorder 18 records imagingmode information (whether auto-focus imaging mode or manual focusimaging mode) along with the image signal to the internal memory and/orremovable memory on the basis of the command of the image recordingcontroller 19.

Upon completion of the exposure, the imaging sensor drive controller 12reads image data from the imaging sensor 11, and after specific imageprocessing, image data is outputted via the body microcomputer 10 to theimage display controller 21. Consequently, the captured image isdisplayed on the display unit 20.

Also, upon completion of the exposure, the shutter unit 33 is reset toits initial position by the body microcomputer 10. The bodymicrocomputer 10 issues a command to the lens microcomputer 40 for theaperture drive controller 42 to reset the aperture unit 62 to its openposition, and a reset command is sent from the lens microcomputer 40 tothe various units. Upon completion of this resetting, the lensmicrocomputer 40 tells the body microcomputer 10 that resetting iscomplete. After the resetting completion information has been receivedfrom the lens microcomputer 40, and after a series of post-exposureprocessing has been completed, the body microcomputer 10 confirms thatthe shutter button 30 is not being pressed, and the imaging sequence isconcluded.

(5) Moving Picture Capture

The digital camera 1 also has the function of capturing moving pictures.In moving picture imaging mode, image data is produced by the imagingsensor 11 at a specific period, and the image data thus produced isutilized to continuously carry out auto-focusing by contrast detectionmethod. In moving picture imaging mode, if the shutter button 30 ispressed, or if the moving picture capture operation button 24 ispressed, a moving picture is recorded to the image recorder 18, and whenthe shutter button 30 or the moving picture capture operation button 24is pressed again, recording of the moving picture by the image recorder18 is stopped.

Features Related to Optical System Layout

The layout of the optical system of the digital camera 1 described aboveare as follows.

(1)

With this digital camera 1, since the focus lens unit 75 moves in the Zaxis direction (a direction parallel to the optical axis AZ) along withthe sixth lens group unit 77, the focus lens unit 75 can be moved withrespect to the imaging sensor 11 by the amount of movement of the sixthlens group unit 77 with respect to the imaging sensor 11. Consequently,a large amount of drive of the focus lens unit 75 can be ensured eventhough there is not much space in front of and behind the focus lensunit 75. That is, the interchangeable lens unit 2 can be more compact.

Furthermore, since the sixth lens group unit 77 is disposed nearest tothe image plane out of the optical system L, the sixth lens group G6 andthe fifth lens group G5 can be more compact than when the sixth lensgroup unit 77 is not disposed nearest to the image plane. Using asmaller fifth lens group G5 allows the drive speed of the focus lensunit 75 to be raised and affords faster auto-focusing.

Thus, with this interchangeable lens unit 2, both faster auto-focusingand a smaller size can be achieved.

(2)

Since the sixth lens group unit 77 is disposed nearest to the imageplane out of the optical system, the focus lens unit 75 is disposed onthe object side of the sixth lens group unit 77. Accordingly, the userwill not touch the focus lens unit 75 in a state in which the lensbarrel has been removed, for example. This prevents the focus lens unit75 from being improperly attached due to the touching of the focus lensunit 75 by the user.

Also, with this lens barrel, since there is no need to mount aprotective glass piece (for protecting the lens) on the imaging sensor11 side, reflection of light by the protective glass can be prevented,which prevents ghosting and flare.

(3)

As shown in FIGS. 7 and 8, the fourth lens group unit 78 is able to movein the optical axis direction within the first movement range F4 usingthe imaging sensor 11 as a reference, and the focus lens unit 75 is ableto move in the optical axis direction within the second movement rangeF5 using the imaging sensor 11 as a reference. Since the second movementrange F5 overlaps the first movement range F4, the size of the opticalsystem L in the Z axis direction can be reduced, which allows theinterchangeable lens unit 2 to be more compact.

(4)

As shown in FIGS. 5 and 7, since the drive shaft 64 a protrudes to thesubject side (the Z axis direction positive side) from the motor body 64s, this prevents the stepping motor 64 d, which is larger than the driveshaft 64 a, from interfering with the fourth lens group unit 78.Consequently, the focus motor 64 and the fourth lens group unit 78 canbe disposed closer together, which allows the interchangeable lens unit2 to be even more compact.

(5)

Since the stepping motor 64 d is disposed to the outside of the sixthlens group G6 in the radial direction, this reduces how much thestepping motor 64 d sticks out from the sixth lens group unit 77 in theZ axis direction. Consequently, the interchangeable lens unit 2 can bemade even more compact.

Features Related to Lens Mount

Features related to the lens mount 95 of the digital camera 1 are asfollows.

(1)

With this digital camera 1, when viewed in the Z axis direction, thelens mount contact 91 is disposed on the opposite side from the focusmotor 64 with respect to the sixth lens group G6. More specifically, asshown in FIGS. 13 and 14, if we let the line that passes through thecenter of the lens mount contact 91 and is perpendicular to the opticalaxis AZ of the sixth lens group G6 be a first imaginary line P, thefocus motor 64 is disposed on the opposite side from the lens mountcontact 91 (within the range M) with respect to a second imaginary lineM1 that is perpendicular to the first imaginary line P and the opticalaxis AZ. Consequently, the focus motor 64 can be disposed at a positionthat is away from the lens mount contact 91, the encoder 64 e of thefocus motor 64 will be less affected by noise generated by the lensmount contact 91, and there will be less of a decrease in the detectionaccuracy of the encoder 64 e.

(2)

The focus motor 64 is disposed at a position that is symmetrical withthe lens mount contact 91 using the optical axis AZ of the sixth lensgroup G6 as a reference. More specifically, as shown in FIGS. 13 and 14,when viewed in the Z axis direction, the focus motor 64 is disposedwithin the range N between the third imaginary line N1 and the fourthimaginary line N2. Therefore, the focus motor 64 can be disposed at aposition that is safely away from the lens mount contact 91, so theencoder 64 e of the focus motor 64 will be less affected by noisegenerated by the lens mount contact 91.

(3)

When viewed in the Z axis direction, the focus motor 64 overlaps thefirst imaginary line, so the focus motor 64 can be safely disposed at aposition that is away from the lens mount contact 91, and the encoder 64e of the focus motor 64 will be less affected by noise generated by thelens mount contact 91.

(4)

Since the electrical substrate 94 is cut out in a portion correspondingto the focus motor 64, even though the electrical substrate 94 isdisposed within the range of movement of the focus motor 64, the focusmotor 64 will not come into contact with the electrical substrate 94.This means that the interchangeable lens unit 2 can be more compact.

(5)

Since the connector 96 a is disposed on the opposite side of the focusmotor 64 with respect to the lens mount contact 91, the focus motor 64can be disposed at a position that is away from the connector 96 a. Theconnector 96 a is similar to the lens mount contact 91 in that it can bea source of noise. Therefore, the focus motor 64 will be less affectedby noise generated by the connector 96 a, and there will be less of adecrease in the detection accuracy of the encoder 64 e.

Features Related to Electronic Tracking

Features related to electronic tracking with the digital camera 1 are asfollows.

(1)

As shown in FIG. 12, with this digital camera 1, the tracking table 100does not have an inflection point between the wide angle end and thetelephoto end. That is, the focus lens unit 75 is driven in onedirection with respect to the sixth lens group unit 77 when the sixthlens group unit 77 is being driven by the zoom ring unit 83 in thatdirection with respect to the fourth lens group unit 78. Accordingly,the direction of movement of the focus lens unit 75 with respect to thesixth lens group unit 77 does not change while the sixth lens group unit77 is being driven in one direction by the zoom ring unit 83.Consequently, there is no decrease in the drive speed of the focus lensunit 75 midway, and the drive speed of the focus lens unit 75 can beraised. That is, control of the focus motor 64 can keep up with fastoperation of the zoom ring unit 83.

(2)

With the infinity tracking table 100, since the starting point positionD is disposed in the center between the first position E1 of the focuslens unit 75 corresponding to the wide angle end and the second positionE2 of the focus lens unit 75 corresponding to the telephoto end, whenthe focus lens unit 75 is driven using the starting point position D asa reference, the focus lens unit 75 can be moved relatively quickly tothe various positions. This allows the state of the digital camera 1 tobe changed smoothly to a state in which imaging is possible.

In particular, since there is a higher probability of capturing thesubject at the infinity position when the user turns on the power to thedigital camera 1 to photograph the subject, the starting point positionD is disposed in the center of the infinity tracking table 100, whichallows the state of the digital camera 1 to be changed smoothly to astate in which imaging is possible.

Other Embodiments

Embodiments are not limited to those discussed above, and variouschanges and modifications are possible without departing from the gistof the present invention. Also, the above embodiments are basically justfavorable examples, and are not intended to limit the present invention,its applications, or the scope of these applications.

(1)

In the above embodiments, the digital camera was capable of capturingboth moving and still pictures, but may instead be capable of capturingjust still pictures, or just moving pictures.

(2)

The digital camera 1 may be, for example, a digital still camera, adigital video camera, a mobile telephone equipped with a camera, or aPDA equipped with a camera.

(3)

The above-mentioned digital camera 1 did not have a quick return mirror,but may have a quick return mirror as do conventional single lens reflexcameras.

(4)

The configuration of the optical system L is not limited to that in theembodiments. For example, the first lens group G1 to the sixth lensgroup G6 may each made up of a plurality of lenses.

Also, in the above embodiment, the sixth lens group unit 77 was disposednearest to the image plane out of the optical system L, but the focuslens unit 75, rather than the sixth lens group unit 77, may instead bedisposed nearest to the image plane out of the optical system L. Hereagain, the fifth lens group G5 can be made more compact, and fasterauto-focusing and a smaller size can both be achieved.

(5)

In the above embodiment, the exposure time to the imaging sensor 11 wascontrolled by operating the shutter unit 33, but the exposure time ofthe imaging sensor 11 may instead be controlled by an electronicshutter.

(6)

In the above embodiment, electronic tracking was performed by the lensmicrocomputer 40, but a command may be sent from the body microcomputer10 to the lens microcomputer 40, and the control of the electronictracking performed on the basis of this command.

(7)

With the tracking table 100, the starting point position D is disposedin the center between the first position E1 of the focus lens unit 75corresponding to the wide angle end and the second position E2 of thefocus lens unit 75 corresponding to the telephoto end. However, as longas the state of the digital camera 1 to be changed smoothly to a statein which imaging is possible, the starting point position D may beshifted somewhat from the center between the first position E1 and thesecond position E2. In other words, the starting point position D shouldbe in the approximate center between the first position E1 and thesecond position E2.

1. A lens barrel detachably mountable to a camera body for forming anoptical image of a subject on an imaging element, comprising: a firstlens unit including a first lens element and a first lens support framesupporting the first lens element; a second lens unit including a secondlens element arranged to vary a focal length by moving relative to thefirst lens element in an optical axis direction, and a second lenssupport frame supporting the second lens element; a focus lens unitincluding a focus lens arranged to vary a focal state of the opticalimage by moving relative to the second lens element in the optical axisdirection, and a focus lens support frame supporting the focus lens; azoom mechanism arranged to relatively move the first lens unit and thesecond lens unit in the optical axis direction, including a zoom controlarranged to be operated by the user, with which the operating forceinputted to the zoom control is mechanically transmitted to at least thesecond lens unit; and a focus actuator being fixed to the second lensunit and configured to electrically drive the focus lens unit relativeto the second lens unit in the optical axis direction, the second lenselement is disposed nearest to an image plane in the optical systemincluding the first lens element, the second lens element, and the focuslens.
 2. The lens barrel according to claim 1, wherein the first lensunit is movable in the optical axis direction within a first movementrange in which the imaging element serves as a reference, the focus lensunit is movable in the optical axis direction within a second movementrange in which the imaging element serves as a reference, and the secondmovement range overlaps the first movement range.
 3. The lens barrelaccording to claim 2, wherein the focus actuator includes an actuatorbody configured to generate a drive force, and a drive shaft arranged totransmit the drive force to the focus lens unit, and the drive shaftprotrudes from the actuator body to the subject side.
 4. The lens barrelaccording to claim 3, wherein the actuator body is disposed to anoutside of the second lens element in a radial direction.
 5. The lensbarrel according to claim 1, wherein the focus actuator includes anactuator body configured to generate a drive force, and a drive shaftarranged to transmit the drive force to the focus lens unit, and thedrive shaft protrudes from the actuator body to the subject side.
 6. Thelens barrel according to claim 5, wherein the actuator body is disposedto an outside of the second lens element in a radial direction.
 7. Animaging device, comprising: the lens barrel according to claim 1; andthe camera body including the imaging element.
 8. The lens barrelaccording to claim 1, wherein the focus lens is disposed between thefirst lens element and the second element.
 9. The lens barrel accordingto claim 1, wherein the lens barrel is an interchangeable lens unitconfigured to be detachably mountable to the camera body.